ASI-1 Manual - MGL Avionics

ASI-1 

Airspeed Indicator (ASI) with 

automatic flight log 

Operating Manual – English 1.06 

Introduction 

The ASI-1 airspeed indicator is a 2 1/4” instrument that provides a wide range airspeed indication in both digital and 

analog formats. Airspeed is based on the pressure generated by a pitot tube system and a static port is provided as well 

for use by high speed aircraft. In addition, the ASI-1 provides a 24 entry automatic flight log that stores the duration of 

each of the last 24 flights, an air-distance trip counter and a current flight timer. Airspeed can be indicated in statute miles 

per hour (mph), kilometers per hour (km/h) or nautical miles per hour (knots) with the air-distance being displayed in 

corresponding units. The analog airspeed display can be scaled according to the aircraft’s flying speed range and 

markers for Vs, Vf, Vno and Vne can be set. ASI sensitivity can be calibrated by the user to cater for errors caused by 

pitot tube placement. The ASI-1 instrument measures airspeed from 16mph to 250mph and is well suited to slower 

aircraft due to very good sensitivity and linearity at low air speeds. 

The ASI-1 also outputs airspeed information via the airtalk protocol for interfacing to the Infinity FF-1 (fuel flow computer 

for single or dual fuel tanks) and the SP-X (AHRS) instruments 

1 Features 

• Measure airspeed from 16mph to 250mph and is well suited to slow aircraft due to very good sensitivity 

and linearity at low air speeds 

• Includes a 24 entry automatic flight log 

• Includes an air-distance trip counter and a flight timer 

• Airspeed units can be set to miles per hour (mph), kilometer per hour (km/h) or nautical miles per hour 

(knots) 

• Contains a programmable low/high airspeed alarm 

• Records maximum airspeed reached in permanent memory 

• Analog bar graph indicating airspeed with markers for Vs, Vf, Vno and Vne 

• Outputs airspeed information via the airtalk protocol for interfacing to the Infinity FF-1 (fuel flow computer 

for single or dual fuel tanks) and the SP-X (AHRS) instruments 

• Standard 2 1/4” aircraft enclosure (can be front or rear mounted) 

• Rotary control plus 2 independent buttons for easy menu navigation and user input 

• External alarm output as well as a red LED illuminates when the alarm has been activated 

• Large backlit graphic LCD with adjustable contrast 

• Wide input supply voltage range of 8 to 30V DC with built in voltage reversal and over voltage protection 

for harsh electrical environments 

• Light weight design 

• 1 year limited warranty

ASI-1 Operating Manual Page 2 

2 ASI-1 Layout 

Backlit Graphic LCD Display: 

Contrast and backlight can be adjusted 

in the menu system 

LED Alarm: 

The red LED will illuminate if the 

airspeed alarm set-point has been 

exceeded 

Pressure Ports: 

Pressure ports connect 

to static and pitot tubes 

Up/F1 Button: 

Up button in menu system 

Start/Stop flight in normal 

mode 

Harness: 

Harness connects to 

power 

Down/F2 Button: 

Down button in menu 

system 

Reset air distance trip 

counter in normal mode 

Rotary Control (Up/Down) & Enter Button: 

Press the rotary control during normal mode to access the menu system. Rotate 

anti/clockwise for up/down menu scrolling. During normal mode rotating the rotary control 

will display the permanent memory maximum recorded airspeed. 

3 Main Display 

Air distance trip 

counter 

Digital airspeed 

Duration of flight 

since take-off 

Analog airspeed display 

Airspeed units 

Airspeed markers 

Airspeed alarm 

Maximum airspeed 

reached marker


3.1 Start/Stop Flight Display 

Press the F1 key during the normal display mode to manually start/stop a flight. This key is only active if the ASI-1 is 

setup to select the manual flight option under the “Flight Log” setup menu. 

3.2 Reset Air Distance Trip Counter Display 

This display can be accessed by pressing the F2 key during the normal display mode. Pressing the F1 key will reset the 

air distance trip counter to zero. Pressing any other key will cause the ASI-1 to resume to the normal display mode. The 

air distance trip counter can still be reset manually even if the pilot selects the automatic resetting of the air distance trip 

counter. 

Note: The air distance trip counter measures distance flown through the air. This is not the same as 

distance flown over the ground unless you are flying at sea level at zero wind speed. The air 

distance shown is subject to under reading at altitude due to decreased air density. 

3.3 Maximum Airspeed Display 

This display can be accessed by rotating the rotary control either clockwise or anticlockwise during the normal display 

mode. Pressing the F1 key again will reset the maximum airspeed to the current airspeed. Pressing any other key will 

cause the ASI-1 to resume back to the normal display mode. To avoid false recordings, the maximum airspeed function is 

only activated 10 seconds after the instrument has powered up. 

Note: The maximum airspeed is stored in non-volatile memory and is 

recalled on power-up.


4 Menu System 

Pressing the rotary control button during the normal display mode will cause the ASI-1 to enter the menu system. Use the 

up/down keys or the rotary control to navigate through the menu system. 

Note: (ADC Values and Calibrate Menus are only visible when powering up the unit and pressing the 

Rotary Control). The text “CALIBRATE” will appear on the intro screen when entering this mode. 

Warning: The Calibrate Menu is for technical personnel only. Changing any values in this menu may 

cause the instrument to display incorrect information, and may require the instrument to be returned to 

the factory for recalibration. 

4.1 Exit Menu 

Pressing the rotary control on this menu item will cause the ASI-1 to exit the menu system. All 

changes made during navigation of the menu system will be saved in non-volatile memory on exiting 

the menu system. If you remove power before exiting the menu the instrument will not save any 

changes. 

4.2 Flight Log 

The ASI-1 uses the following algorithm to determine if a flight is in progress (Detect Mode): If 

airspeed is greater than the preset flight take off airspeed for a duration of 60 seconds or more, a 

flight is started with a logbook entry. The flight ends if airspeed falls below the preset flight take-off 

airspeed for 30 seconds. During a flight the logbook cannot be viewed. 

The above algorithm ensures that touch-and-goes will not result in the end of a flight and a logbook 

entry. Should the instrument be switched off during a flight, this will end the flight and the log will 

reflect the time until the instrument was switched off. Should the instrument be switched on again during a flight, a new 

flight will start for logging purposes. 

Move the highlight over the “DONE” menu item and press the rotary button to return to the main 

menu


Select this function to view the flight log. The flight log contains the duration of 

each of the last 24 logged flights. Duration is displayed in hours and minutes. 

Use the up/down keys or the rotary control to navigate through the log. Empty 

log entries are shown as “-----“. 

Note: You cannot select this function while a flight is in progress. 

Pressing the F1 key will erase all the flight log entries 

Select if you would like the hour to be displayed in decimal fractions (0-99) or minutes (0-59). 

This setting influences the current flight time display and the flight log. 

Select whether you want the ASI-1 to automatically detect a flight or whether the pilot must press the 

F1 key to start/stop a flight. 

This menu option is only shown if the “detect” flight mode is selected. Enter the airspeed that you 

want to start a flight log. 

4.3 Display Setup 

Move the highlight over the “DONE” menu item and press the rotary button to return to the main 

menu 

Select this menu option to adjust the display contrast 

Select this menu option to turn the backlight on or off


4.4 Airspeed Setup 

All the airspeed parameters can be setup here 

Move the highlight over this menu option and press the rotary button to return to the main menu 

This setup allows your instrument to measure the zero airspeed reading of the 

airspeed sensor and set a calibration value internally for this. This is 

equivalent to some mechanical airspeed indicators that have an adjustment to 

set the needle to zero when the aircraft is not moving. You would use this 

function occasionally if you see an airspeed reading when the aircraft is at 

rest. This may be caused by aging of the built in pressure sensor or related electronics. When this function is performed 

make sure that there is no air flow into the pitot tube as this would result in an incorrect internal calibration. 

Pressing the F1 key will zero the airspeed sensor. 

Select the maximum value that you want the airspeed analog bar graph display to show. This can 

give you increased display resolution. 

Select whether you want the low air speed alarm to be turned on or off. The low airspeed alarm is 

only activated once a flight has started. 

Enter the low airspeed set-point for when the alarm must activate. Any speed below this value will 

activate the alarm. 

Select whether you want the high air speed alarm to be turned on or off. 

Enter the high airspeed set-point for when the alarm must activate. Any speed above this value will 

activate the alarm. 

Select your preferred units. You can select statute miles, kilometers or nautical miles. According 

to this selection your airspeed will be indicated in mph, km/h or knots. 

This function can be used to select the signal filter time constant. Selections are “fast” or “slow”. This 

selection influences the rate at which your ASI can change its reading. If you have an installation 

that suffers from strong turbulence at the pitot tube, select “slow”. If you have a very clean airflow in 

front of the pilot tube you can select “fast” which will give you a faster response to airspeed changes. 

Select if you want the air-distance counter to reset automatically at the start of a flight or if you want 

to reset manually only. 

Note: You can reset the air distance counter at any time regardless of this setting.


You can set up a marker on the analog airspeed display for Vs. Vs would be your stall speed or 

minimum safe flying speed. You may also choose to use this marker as your approach speed. 

You can set up a marker on the analog airspeed display for Vf. Vf is your maximum flap speed. 

You can set up a marker on the analog airspeed display for Vno. Vno is the maximum 

maneuvering speed or top end of the normal operating speed range. 

You can set up a marker on the analog airspeed display for Vne. Vne is the never exceed maximum 

speed. 

4.5 ADC Values 

Note: This menu item is for technical personnel only, and is not displayed during the normal 

operation of the instrument. Please see section 4 above on how to access this menu item. 

This menu displays the ADC values that have been read from the pressure sensor. 

4.6 Calibrate 

Note: This menu item is for technical personnel only, and is not displayed during the normal 

operation of the instrument. Please see section 4 above on how to access this menu item. Consult 

your local dealer or factory before entering this menu. 

This function is used to calibrate your airspeed indicator. During the factory calibration a factor has 

been determined and entered here that will give you accurate airspeed, provided your pitot tube is 

not influenced by pressure effects caused by airflow around your airframe. The calibration is 

displayed in % of the reading, you can increase or decrease the reading if required to help cancel 

out under or over reading of the airspeed indicator on your aircraft. The original calibration factor has 

been written onto the back of your instrument.


5 Loading Factory default settings 

Pressing and holding the F1 and F2 key simultaneously on power up will cause the ASI-1 to load preprogrammed factory 

default settings. The following screen will be displayed: 

6 Operating the alarms 

If the alarm is activated, the corresponding item on the display will flash. At the same time the externally available alarm 

switch will close. The switch will remain closed until any button is pressed to acknowledge the alarm or until the 

condition(s) that activated the alarm no longer exist. The alarm output can be used to switch an external alarm indicator. 

The external alarm switch is an open collector transistor switch to ground with a maximum rating of 0.5A DC. It is possible 

to wire the alarm contacts of several Stratomaster instruments in parallel should this be desired. To avoid false activation 

of the alarms, the alarm function is only active 10 seconds after the instrument has powered up. 

7 Cleaning 

The unit should not be cleaned with any abrasive substances. The screen is very sensitive to certain cleaning materials 

and should only be cleaned using a clean, damp cloth. 

Warning: The ASI-1 is not waterproof, serious damage could occur if the unit is exposed to 

water and/or spray jets. 

8 Specifications 

Operating Temperature Range 

Storage Temperature Range 

Humidity 

Power Supply 

Current Consumption 

Display 

ADC 

Dimensions 

Enclosure 

Weight 

Alarm contact current rating 

Non-volatile memory storage 

Airspeed range 

Airspeed resolution 

Measurement accuracy 

Airtalk protocol 

-10ºC to 50ºC (14ºF to 122ºF) 

-20ºC to 80ºC (-4ºF to 176ºF) 


9 Installation 

Connect a pitot tube to the “pressure port” and if required connect the static port. Pitot tubes are found in a large variety at 

your aircraft parts shop, in mail order catalogs or you can make your own. Contrary to popular belief, pitot tubes are not 

carefully designed and calibrated but are simple orifices or tubes that get pointed in the direction that you are flying. The 

forward movement of the aircraft causes air to dam inside the pitot tube. This increases the pressure inside the tube. Most 

small aircraft such as ultralights or microlights do not require a connection to a static port. In these cases, simply leave the 

static port open. Ensure however that the static port does not receive pressurized air due to the forward movement of the 

aircraft. Be especially critical of your pod or panel if you do not use a static port. Any build up of a pressure differential due 

to ram air or suction can lead to large errors of the indicated airspeed. Static ports are usually mounted at a strategic 

position on the rear side of the aircraft fuselage for faster, pressurized aircraft. Suitable pitot tubes can be made from a 

short piece of hollow aluminum or copper piping. Length and diameter are not important. Ensure that the front of the pitot 

tube has a suitable chamfer if you use thick walled tubing or you may introduce a speed reading error if you have a faster 

aircraft. 

Example cross-section of thick walled pitot tube. 

Suitable connection hose for both pitot tube and static port can be obtained from a hardware store or even a pet shop. 

Good quality tubing is often used for fish tanks and it has just the right diameter. 

Please note that this kind of tubing is not advised for pressurized aircraft. In this case you would need to obtain aircraft 

grade tubing of suitable diameter. You would also have to use hose clamps to fasten the hose onto the ASI-1 pitot and 

static ports. The ASI-1 allows you to calibrate the airspeed reading. This is done under the “Calibrate” menu item. The 

main reason for this is to be able to remove errors introduced due to the airflow around your aircraft which may have an 

effect on your pitot tube pressure. 

9.1 ASI-1 DB9 Cable connections 

9.2 Pressure Port Dimensions 

DB 9 Pin Color Function 

1 Black Ground 

4 NC Airtalk communication 

Used for firmware upgrading and interfacing 

to the FF-1/SP-X (Airtalk speed message) 

6 Red 8-30Vdc power 

9 White Alarm Output 

A 

B 

C 

D 

Inches 

Millimeters 

Min Max Min Max 

0.248 0.278 6.30 7.06 

0.420 0.440 10.67 11.18 

0.182 0.194 4.62 4.93 

0.310 0.330 7.87 8.38


9.3 Connection Diagram 

The use of an external 1A fuse is recommended. Connect the supply terminals to your aircrafts power supply. The ASI-1 

can be used on both 12V and 24V without the use of any pre-regulators. Ensure that the supply voltage will not drop 

below 8V during operation as this may result in incorrect voltage and or current readings. 

10 Warranty 

This product carries a warranty for a period of one year from date of purchase against faulty workmanship or defective 

materials, provided there is no evidence that the unit has been mishandled or misused. Warranty is limited to the 

replacement of faulty components and includes the cost of labour. Shipping costs are for the account of the purchaser. 

Damage as a result of applying excessive pressure to the pressure ports are excluded from warranty. 

Note: Product warranty excludes damages caused by unprotected, unsuitable or incorrectly wired 

electrical supplies and/or sensors, and damage caused by inductive loads.


11 Disclaimer 

Operation of this instrument is the sole responsibility of the purchaser of the unit. The user must make themselves familiar 

with the operation of this instrument and the effect of any possible failure or malfunction. 

This instrument is not certified by the FAA. Fitting of this instrument to certified aircraft is subject to the rules and 

conditions pertaining to such in your country. Please check with your local aviation authorities if in doubt. This instrument 

is intended for ultralight, microlight, homebuilt and experimental aircraft. Operation of this instrument is the sole 

responsibility of the pilot in command (PIC) of the aircraft. This person must be proficient and carry a valid and relevant 

pilot’s license. This person has to make themselves familiar with the operation of this instrument and the effect of any 

possible failure or malfunction. Under no circumstances does the manufacturer condone usage of this instrument for IFR 

flights. 

The manufacturer reserves the right to alter any specification without notice. 

Other instruments in the Stratomaster Infinity series 

ALT-1 Precision encoding altimeter and vertical speed indicator 

ALT-2 Precision encoding altimeter and vertical speed indicator with a serial RS232 

transponder output 

ASI-1 Airspeed indicator (ASI) with automatic flight log 

ASX-1 Encoding aviation altimeter with serial output and airspeed indicator (ASI) 

AV-1 Artificial horizon and magnetic compass indicator 

BAT-1 Battery voltage and current monitor 

E-3 Universal engine monitor 

FF-1 Fuel Computer (single or dual fuel tanks) 

GF-1 +-10G tilt compensated dual range G-force meter 

MAP-1 Manifold pressure and RPM Indicator 

RV-1 Universal engine RPM and rotor RPM Indicator 

RV-2 Universal turbine RPM / RPM factor display 

RTC-2 Aviation real time clock (RTC) and outside air temperature (OAT) display 

TC-1 4-Channel thermocouple indicator 

TP-1 Universal temperature and pressure gauge

ASI-1 Manual - MGL Avionics

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